Shackle destruction test, and thoughts . . .

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The lads at Unsealed4x4 in Australia recently released this video, which shows three types of shackle being tested to destruction. It’s always interesting to see stuff destroyed in controlled conditions, and there is some value here. 

To summarize their results:

  • The tiny unrated shackle snapped at 4,485 kg (9,888 pounds)
  • The rated steel TJM shackle—a standard 4.75-ton WLL example (9,500 pounds if it is a U.S. ton, 10,469 pounds if a metric ton)—identical in spec to what many of us carry, failed at an impressive 35,219 kg, or 77,644 pounds. That handily surpasses the industry standard 6:1 safety margin for rated shackles.
  • The soft shackle, rated at 8,000 kg (17,637 pounds) broke at 9,327 kg or 20,562 pounds when pulled over two rounded edges. However, it broke at just 6,930 kg (15,278 pounds) when stressed over one sharp edge, and at 7,686 kg (16,945 pounds) with a sheath in place between the shackle and the edge. Soft shackles do not yet have an industry standard safety margin; users are expected to abide by the working load limit (WLL) or minimum breaking strength (MBS), which this one easily exceeded when deployed carefully. The below-rating breakages pointed out the vulnerability of soft shackles when stressed over a sharp edge, such as many bumper shackle mounts have.

Several thoughts come to mind:

  1. Testing one of each piece means zero statistically. The TJM shackle could have been an outstanding example of its type while one of the soft shackles might have had a flaw (not that they in any way “failed” except as should be expected), or vice versa.
  2. The much smaller unrated shackle actually performed pretty well, and would probably have held up in a majority of winching situations—not that it would be a good idea to try it. A much fairer comparison would have been to test an unrated shackle of similar size to the TJM. 
  3. While the TJM shackle failed quite suddenly (admittedly at a very high load), the soft shackles seemed to give clear visual warning of their imminent demise had a spotter been watching. In fact it appeared one of them could have been re-knotted and reused in an emergency situation.

While as I said this test is not statistically significant, I believe it accurately reflects the strengths and weaknesses of soft shackles. Their greater safety factor is a huge point in their favor—just as with synthetic winch line, there is far less kinetic energy stored in a soft shackle than in its steel counterpart. (Notice that the engineers didn't even bother to place a guard over the soft shackle when they tested it.) However, they are not ideal in every situation. In our driveway right now are two vehicles—our FJ40 and our Tacoma—which have shackle mounts I would never hook to with a soft shackle. 

 The FJ40's rear shackle mounts are very sharp-edged. No problem for a steel shackle if the pin fits properly.

The FJ40's rear shackle mounts are very sharp-edged. No problem for a steel shackle if the pin fits properly.

 Likewise, this aftermarket shackle mount for the Tacoma has very sharp edges.

Likewise, this aftermarket shackle mount for the Tacoma has very sharp edges.

Soft shackles are a great advance in safety and ease of handling, but only when used in appropriate circumstances. A complete recovery kit should include both hard and soft versions.